Passivating pinholes for large-area and high-efficiency silicon solar cells with tunnel oxide passivated contact

The tunnel oxide passivated contact (TOPCon) solar cell is poised to dominate silicon photovoltaics, yet the atomic-scale nature of pinholes—local disruptions in the SiOx layer enabling direct conduction—remains unresolved despite its critical importance for device performance. Here, using spherical aberration-corrected transmission electron microscopy, the TOPCon interface is uncovered at the atomic level, revealing two distinct pinhole types: recombinational pinholes with oxygen-depleted Si–Si contacts, and previously unknown passivating pinholes that retain sufficient oxygen to passivate dangling bonds while enabling carrier tunneling. These passivating pinholes exhibit cross-sectional sizes of approximately 1.6 ± 0.2 nm × 1.4 ± 0.3 nm and an area density of 2×1012 cm-2. Fischer model analysis demonstrates that pinhole passivation, not geometry, governs device performance. Translating these insights, industrial large-area (333.3 cm2) TOPCon solar cells achieve certified efficiencies of 25.40% and open-circuit voltages of 738.7 mV. Our findings provide atomic-level insights into the TOPCon interface and offer direct guidance for fabricating high-efficiency solar cells. Tunnel oxide passivating contact solar cells face unresolved questions about the atomic scale nature of pinholes that limit performance. The authors use aberration corrected transmission electron microscopy to reveal two pinhole types and showing that oxygen-based passivation rather than pinholes geometry drives efficiency.